From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>,
"Marcelo Tosatti" <mtosatti@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>,
qemu-devel@nongnu.org, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] invtsc + migration + TSC scaling
Date: Mon, 17 Oct 2016 18:24:38 +0200 [thread overview]
Message-ID: <72b8c6b3-f08a-735a-e283-99d0195dcf7d@redhat.com> (raw)
In-Reply-To: <20161017145008.GA2307@potion>
On 17/10/2016 16:50, Radim Krčmář wrote:
> 2016-10-17 07:47-0200, Marcelo Tosatti:
>> On Fri, Oct 14, 2016 at 06:20:31PM -0300, Eduardo Habkost wrote:
>>> I have been wondering: should we allow live migration with the
>>> invtsc flag enabled, if TSC scaling is available on the
>>> destination?
>>
>> TSC scaling and invtsc flag, yes.
>
> Yes, if we have well synchronized time between hosts, then we might be
> able to migrate with a TSC shift that cannot be perceived by the guest.
>
> Unless the VM also has a migratable assigned PCI device that uses ART,
> because we have no protocol to update the setting of ART (in CPUID), so
> we should keep migration forbidden then.
We don't publish the ART leaf at all, do we?
>> 1) Migration: to host with different TSC frequency.
>
> We shouldn't have done this even now when emulating anything newer than
> Pentium 4, because those CPUs have constant TSC, which only lacks the
> guarantee that it doesn't stop in deep C-states:
Right, but:
>> since Linux guests use kvmclock and Windows guests use Hyper-V
>> enlightenment, it should be fine to disable 2).
... and 1 too.
We should also blacklist the TSC deadline timer when invtsc is not
available.
Paolo
next prev parent reply other threads:[~2016-10-17 16:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-14 21:20 [Qemu-devel] invtsc + migration + TSC scaling Eduardo Habkost
2016-10-17 9:47 ` Marcelo Tosatti
2016-10-17 14:50 ` Radim Krčmář
2016-10-17 16:24 ` Paolo Bonzini [this message]
2016-10-17 21:11 ` Eduardo Habkost
2016-10-17 23:58 ` Marcelo Tosatti
2016-10-18 13:41 ` Paolo Bonzini
2016-10-18 17:09 ` Marcelo Tosatti
2016-10-18 20:52 ` Radim Krčmář
2016-10-18 21:05 ` Eduardo Habkost
2016-10-19 13:27 ` Radim Krčmář
2016-10-19 13:55 ` Eduardo Habkost
2016-10-19 15:42 ` Radim Krčmář
2016-10-19 17:42 ` Eduardo Habkost
2016-10-18 13:48 ` Radim Krčmář
2016-10-18 13:36 ` Radim Krčmář
2016-10-18 13:38 ` Radim Krčmář
2016-10-17 17:20 ` Marcelo Tosatti
2016-10-18 13:27 ` Radim Krčmář
2016-10-18 9:04 ` Dr. David Alan Gilbert
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